1. Field of the Invention
The present invention relates to a device for analyzing an alternating voltage or current signal that nay have a D.C. voltage or D.C. current component.
2. Prior Art
It is known that various measured variables can be determined by analyzing periodically varying alternating voltage or alternating current signals. Thus for example rotational speed or angular position measurements are performed with the help of inductive sensors, which detect a rotating body with a characteristic surface. Since the sensor is fixed in such measurements, a periodically oscillating voltage is induced by a rotating body in the sensor, for example an inductive sensor with a measuring coil. From the period of these signals the rotational speed or its angular position is determined with a suitable surface formed on the rotating body.
These devices for producing a rotation speed-dependent signal train are, for example, known in connection with the determination of angular position of the crankshaft or camshaft of an internal combustion engine. Usually a ferromagnetic wheel is connected with the concerned shaft. It is monitored or detected with the help of a sensor surrounding a coil. Since the induced voltage is, for one thing, strongly dependent on its amplitude and, for another, can be superimposed with an interfering voltage, measures are required which guarantee a clean separation of the useful signal from the background signal.
A device for acquiring pulse signals that permits separation of the useful signal from additional D.C. voltage components is described in German Patent DE-PS 42 05 352. This separation is performed with the help of offset compensation and a low-pass filter. Furthermore the low- pass-filtered output signal is compared with the unfiltered input signal in a comparator and thus a largely noise-free output signal is obtained at the output of the comparator. This circuit may however still not be optimally adjusted for different signals to be evaluated, and it does not have dynamic signal tunability.